Structural and optical properties of coherent GaN islands grown on 6H-SiC(0001)-(√3×√3)

Abstract

Coherent islands of GaN with base widths in the range of 100 to 500 nm were grown on 6H-SiC(0001)-(√3×√3) surfaces via the vapor–liquid–solid (VLS) mechanism. The microstructure of GaN islands was studied by high-resolution cross-sectional transmission electron microscopy. The morphological details of the islands were imaged by atomic force microscopy and the same assembly of islands was identified in a scanning electron microscope in which site-specific cathodoluminescence (CL) spectroscopy was conducted on individual islands. The broadening of the CL linewidths together with the shift to lower wave numbers in the E2 Raman mode detected by micro-Raman spectroscopy suggest the existence of tensile strain in the GaN islands. The strain is due to the heavy Si doping of the GaN islands by Si adatoms on the (√3×√3) substrate surface during the VLS growth process.